1. Field of Invention
The present invention relates to gear reducing devices, and more particularly but not by way of limitation, to improved speed reducing assemblies of the type used to power oil production pumping units.
2. Prior Art
In the production of oil utilizing downhole pumps, it is common to utilize a surface apparatus having a reciprocating walking beam, one end of which being referred to as a horse's head. Attached to the horse's head is one end of a rod strand that extends down through an oil well tubing, the other end of the rod strand being attached to a reciprocating action downhole fluid pump. As the walking beam is oscillated about its supporting pivot post, the horse's head causes the rod strand to move alternately upward and then downward, stroking the downhole pump and lifting fluid up the tubing.
A walking beam of the type described is usually powered by an internal combustion engine or by an electric motor, each of which generate power at relatively high rotational speeds. It is common to couple the power input of such plants to a speed reducer which in turn is connected to apparatus that cause the walking beam to oscillate at a much reduced rate. For example, an electric motor output of 1750 r.p.m. might power a walking beam that is operating at 20 strokes per minute.
The amount of power that must be transmitted to the walking beam of a pumping unit has in the past usually required multiple strands of belts or chains in order to transmit the required pumping horsepower, since standard belts or chains are rated at increments of the required power, and by the use of multiple strands, more precise and economical matching of power transmission requirements can be achieved.
There are problems with using multiple strands of belts or chains, as the individual strands tend to relax and stretch at independent rates. It is difficult to continuously keep such strands evenly tensioned so that all of the strands share the power transmission. In the past, the use of multiple strands or webs of chains proved very impractical, as it seemed a near impossible task to determine whether the strands or web were evenly tensioned, and as wear set in, the uneven tensioning condition caused severe wear to increase at near geometric age progression. This almost altogether discouraged the use of chains in speed reducers for oil well pumping units, and as a consequence, most such pumping units were constructed to have sheaves and fiber belts. While fiber belts introduced considerable stretch, this could be offset somewhat by mounting the bearing blocks supporting the drive shafts on tracks so that the supporting shaft could be canted to provide means to obtain even tensioning of the individual belt strands. However, such belts required continuous attention to tension adjustment, and the belts had sheave slippage not encountered in the positive dripping afforded by the use of chains and sprockets.